The long-term goal of the proposed research is to increase our unerstanding of spatial and temporal interactions in the procecsing of color information. A series of psychophysical experiments are designed to assess the visual effects of the simultaneous or successive presentation of chromatic stimuli which are either continguous or superposed in space. The experimental methodology requires the complete specification of the physical characteristics of the visual stimulus. Increment sensitivity to a spot of light superposed upon background fields of varying physical properties is the main dependent variable. Relevant anatomical and physiological data obtained from both human and animal subjects will contribute to our understanding of the human psychophyscal data.